[slurm-users] MPI jobs via mirun vs. srun through PMIx.

[Loris Bennett]

Philip Kovacs <pkdevel at yahoo.com> writes:

>>according to https://slurm.schedmd.com/mpi_guide.html I have built
>>Slurm 19.05 with PMIx support enabled and it seems to work for both,
>>OpenMPI and Intel MPI. (I've also set MpiDefault=pmix in slurm.conf.)
>
>>But I still don't get the point. Why should I favour `srun ./my_mpi_program´ 
>>over `mpirun ./my_mpi_program´? For me, both seem to do exactly the same 
>>thing. No? Did I miss something?
>
>>Best regards
>>Jürgen
>
> Running a single job in isolation doesn't properly illustrate what slurm does in the larger sense.
> How do you fairly allocate and constrain the resources of an HPC installation when 1,000 jobs need
> to run, not just 1?  How do you schedule the jobs?  How do you keep track of the resources used so
> that charge-back or billing can occur?  It's not about the ant -- it's about the colony.

I think Jürgen may well be aware of what Slurm does in the larger sense.
I suspect the question, which I also have, is more like:

  "What difference does it make whether I use 'srun' or 'mpirun' within
   a batch file started with 'sbatch'."

Cheers,

Loris

-- 
Dr. Loris Bennett (Mr.)
ZEDAT, Freie Universität Berlin         Email loris.bennett at fu-berlin.de